Boat Danish from Bulgaria

[niki12]

From the site I get m40c Tohatsu 1.92. With 14p propeller I reached 44mph. measured by GPS

http://www.tohatsu.co.jp/en/boat/products/m40csp.html

According to data from the site at 10% slip out that the engine speed is 7200rpm to 44mph. Even if it reached 60mph, I suppose 55mph is no problem with the propeller 19p. I do not know whether it is healthy for the engine.

[niki12]

From the site I get m40c Tohatsu 1.92. With 14p propeller I reached 44mph. measured by GPS
According to data from the site at 10% slip out that the engine speed is 7200rpm to 44mph. Even if it reached 60mph, I suppose 55mph is no problem with the propeller 19p. I do not know whether it is healthy for the engine.

[zul8tr]

The calculation of 7200 rpm with assumed 10% slip is theoretical. However since you are using assumed 10% slip with measured 44 mph and 14p the calculation correctly yeilds 7200 rpm. But since you did not measure the 7200rpm with a tachometer I doubt that the engine is turning that rpm and in reality there is greater than 10% slip with a lower rpm for your setup.

Remember I said that 10% is about right your light setup but in your case it is probably greater since I doubt your engine is doing 7200 rpm. You need to get a tachometer so you can calculate the actual slipr. Remember the equation for speed has pitch, rpm, gear ratio and slip. You can only have 1 unknown to do the calculation. In your example you have 2 unknowns rpm and slip with speed, gear ratio and pitch known. You need to know rpm to calcutate slip.

[FrenchPhil]

You really need to get the motor up. The cavitation plate should be at least level with the hull bottom, but you'll probably have to go higher but with a nosecone or water pickup for more speed..

[bajarick]

From the site I get m40c Tohatsu 1.92. With 14p propeller I reached 44mph. measured by GPS
According to data from the site at 10% slip out that the engine speed is 7200rpm to 44mph. Even if it reached 60mph, I suppose 55mph is no problem with the propeller 19p. I do not know whether it is healthy for the engine.

I been following this thread and its nice to see a REAL boat being saved!!

Keep up the good work - looks like a lot of fun!!

Im saving an rc boat (see saved from the junkpile) that started life as an inboard and Im converting it to outboard - check out the rc boat threads - "SK60 Drag boat conversion".

Its fun to bring home something old and make it new again!